Order of trigger firing.
SQL>
SQL> CREATE TABLE session (
2 department CHAR(3),
3 course NUMBER(3),
4 description VARCHAR2(2000),
5 max_lecturer NUMBER(3),
6 current_lecturer NUMBER(3),
7 num_credits NUMBER(1),
8 room_id NUMBER(5)
9 );
Table created.
SQL>
SQL> INSERT INTO session(department, course, description, max_lecturer, current_lecturer, num_credits, room_id)
2 VALUES ('HIS', 101, 'History 101', 30, 11, 4, 20000);
1 row created.
SQL>
SQL> INSERT INTO session(department, course, description, max_lecturer, current_lecturer, num_credits, room_id)
2 VALUES ('HIS', 301, 'History 301', 30, 0, 4, 20004);
1 row created.
SQL>
SQL> INSERT INTO session(department, course, description, max_lecturer, current_lecturer, num_credits, room_id)
2 VALUES ('CS', 101, 'Computer Science 101', 50, 0, 4, 20001);
1 row created.
SQL>
SQL> INSERT INTO session(department, course, description, max_lecturer, current_lecturer, num_credits, room_id)
2 VALUES ('ECN', 203, 'Economics 203', 15, 0, 3, 20002);
1 row created.
SQL>
SQL> INSERT INTO session(department, course, description, max_lecturer, current_lecturer, num_credits, room_id)
2 VALUES ('CS', 102, 'Computer Science 102', 35, 3, 4, 20003);
1 row created.
SQL>
SQL> INSERT INTO session(department, course, description, max_lecturer, current_lecturer, num_credits, room_id)
2 VALUES ('MUS', 410, 'Music 410', 5, 4, 3, 20005);
1 row created.
SQL>
SQL> INSERT INTO session(department, course, description, max_lecturer, current_lecturer, num_credits, room_id)
2 VALUES ('ECN', 101, 'Economics 101', 50, 0, 4, 20007);
1 row created.
SQL>
SQL> INSERT INTO session(department, course, description, max_lecturer, current_lecturer, num_credits, room_id)
2 VALUES ('NUT', 307, 'Nutrition 307', 20, 2, 4, 20008);
1 row created.
SQL>
SQL> INSERT INTO session(department, course, description, max_lecturer, current_lecturer, num_credits, room_id)
2 VALUES ('MUS', 100, 'Music 100', 100, 0, 3, NULL);
1 row created.
SQL>
SQL>
SQL>
SQL> CREATE TABLE MyTable (
2 num_col NUMBER,
3 char_col VARCHAR2(60)
4 );
Table created.
SQL>
SQL>
SQL> CREATE SEQUENCE trig_seq
2 START WITH 1
3 INCREMENT BY 1;
Sequence created.
SQL>
SQL> CREATE OR REPLACE PACKAGE TrigPackage AS
2 v_Counter NUMBER;
3 END TrigPackage;
4 /
Package created.
SQL>
SQL> CREATE OR REPLACE TRIGGER sessionBeforeUpdate
2 BEFORE UPDATE ON session
3 BEGIN
4 TrigPackage.v_Counter := 0;
5
6 INSERT INTO MyTable (num_col, char_col)
7 VALUES (trig_seq.NEXTVAL,
8 'Before Statement: counter = ' || TrigPackage.v_Counter);
9
10 TrigPackage.v_Counter := TrigPackage.v_Counter + 1;
11 END sessionBeforeUpdate;
12 /
Trigger created.
SQL>
SQL> CREATE OR REPLACE TRIGGER sessionAfterStatement1
2 AFTER UPDATE ON session
3 BEGIN
4 INSERT INTO MyTable (num_col, char_col)
5 VALUES (trig_seq.NEXTVAL,
6 'After Statement 1: counter = ' || TrigPackage.v_Counter);
7
8 TrigPackage.v_Counter := TrigPackage.v_Counter + 1;
9 END sessionAfterStatement1;
10 /
Trigger created.
SQL>
SQL> CREATE OR REPLACE TRIGGER sessionAfterStatement2
2 AFTER UPDATE ON session
3 BEGIN
4 INSERT INTO MyTable (num_col, char_col)
5 VALUES (trig_seq.NEXTVAL,'After Statement 2: counter = ' || TrigPackage.v_Counter);
6
7 TrigPackage.v_Counter := TrigPackage.v_Counter + 1;
8 END sessionAfterStatement2;
9 /
Trigger created.
SQL>
SQL> CREATE OR REPLACE TRIGGER sessionBeforeRow1
2 BEFORE UPDATE ON session
3 FOR EACH ROW
4 BEGIN
5 INSERT INTO MyTable (num_col, char_col)
6 VALUES (trig_seq.NEXTVAL,
7 'Before Row 1: counter = ' || TrigPackage.v_Counter);
8
9 -- Increment for the next trigger.
10 TrigPackage.v_Counter := TrigPackage.v_Counter + 1;
11 END sessionBeforeRow1;
12 /
Trigger created.
SQL>
SQL> CREATE OR REPLACE TRIGGER sessionBeforeRow2
2 BEFORE UPDATE ON session
3 FOR EACH ROW
4 BEGIN
5 INSERT INTO MyTable (num_col, char_col)
6 VALUES (trig_seq.NEXTVAL,
7 'Before Row 2: counter = ' || TrigPackage.v_Counter);
8
9 TrigPackage.v_Counter := TrigPackage.v_Counter + 1;
10 END sessionBeforeRow2;
11 /
Trigger created.
SQL>
SQL> CREATE OR REPLACE TRIGGER sessionBeforeRow3
2 BEFORE UPDATE ON session
3 FOR EACH ROW
4 BEGIN
5 INSERT INTO MyTable (num_col, char_col)
6 VALUES (trig_seq.NEXTVAL,
7 'Before Row 3: counter = ' || TrigPackage.v_Counter);
8
9 TrigPackage.v_Counter := TrigPackage.v_Counter + 1;
10 END sessionBeforeRow3;
11 /
Trigger created.
SQL>
SQL> CREATE OR REPLACE TRIGGER sessionAfterRow
2 AFTER UPDATE ON session
3 FOR EACH ROW
4 BEGIN
5 INSERT INTO MyTable (num_col, char_col)
6 VALUES (trig_seq.NEXTVAL,
7 'After Row: counter = ' || TrigPackage.v_Counter);
8
9 TrigPackage.v_Counter := TrigPackage.v_Counter + 1;
10 END sessionAfterRow;
11 /
Trigger created.
SQL>
SQL> DELETE FROM MyTable;
0 rows deleted.
SQL>
SQL> UPDATE session
2 SET num_credits = 4
3 WHERE department IN ('HIS', 'CS');
4 rows updated.
SQL>
SQL> SELECT *
2 FROM MyTable
3 ORDER BY num_col;
NUM_COL CHAR_COL
---------- ------------------------------------------------------------
1 Before Statement: counter = 0
2 Before Row 3: counter = 1
3 Before Row 2: counter = 2
4 Before Row 1: counter = 3
5 After Row: counter = 4
6 Before Row 3: counter = 5
7 Before Row 2: counter = 6
8 Before Row 1: counter = 7
9 After Row: counter = 8
10 Before Row 3: counter = 9
11 Before Row 2: counter = 10
NUM_COL CHAR_COL
---------- ------------------------------------------------------------
12 Before Row 1: counter = 11
13 After Row: counter = 12
14 Before Row 3: counter = 13
15 Before Row 2: counter = 14
16 Before Row 1: counter = 15
17 After Row: counter = 16
18 After Statement 2: counter = 17
19 After Statement 1: counter = 18
19 rows selected.
SQL>
SQL>
SQL> DROP SEQUENCE trig_seq;
Sequence dropped.
SQL>
SQL> drop table mytable;
Table dropped.
SQL>
SQL> drop table session;
Table dropped.
SQL>
SQL>
| 1. | Avoid the mutating table error. |